The captain of the Air India Express Boeing 737-800 that crashed at Mangalore on 22 May had been sleeping during the flight and was disorientated during the final approach, according to a government official quoted anonymously by the Indian media.
The accident report has been submitted to India's civil aviation minister Praful Patel, who has said he will not make a statement until he has had time to consider it.
Air India will not comment because the report has yet to be presented to Parliament before it is released.
There were 166 people on the flight when it overran the end of Mangalore's runway and plunged down a steep slope. Both pilots were killed and only eight people survived.
The leaked report is alleged to say that the cockpit voice recorder recorded loud snoring from the captain during the cruise. The government official quoted in the press says that when the captain was flying the approach to Mangalore his reactions were sluggish, and the co-pilot told him more than once to abandon the approach and go around, but he persisted with the landing.
Mangalore's airport is on a hilltop with a steep slope at either end of the runway.